This invention relates in general to machines for performing hydroforming operations on workpieces. In particular, this invention relates to an improved structure for a mechanical press that is adapted to perform a hydroforming operation on a workpiece.
Mechanical presses are well known machines that are commonly used to manufacture a wide variety of workpieces including, for example, relatively large or thick-walled workpieces such as side rails, cross members, and other components for vehicle frame assemblies. A typical mechanical press includes a stationary portion (typically referred to as a bed) having a first die section secured thereto, a movable portion (typically referred to as a slide) having a second die section secured thereto, and an actuating mechanism for selectively moving the slide toward and away from the bed. When the slide is moved toward the bed, the first and second die sections engage the workpiece and exert forces thereon to mechanically deform it into a desired shape. When the slide is moved away from the bed, the first and second die sections are spaced apart from one another to allow the deformed workpiece to be removed and permit the next workpiece to be deformed to be inserted therebetween.
Traditionally, the workpieces that are formed using conventional mechanical presses are stamped from flat stock or open channel structural numbers, i.e., structural members that have a non-continuous cross sectional shape (for example, a U-shaped or C-shaped channel member). The formation of a workpiece from such flat stock and open channel structural members has functioned satisfactorily for many years. However, more recently, it has been found desirable to form a workpiece from a closed channel structural member, i.e., a structural member having a continuous cross sectional shape (for example, a tubular or box-shaped channel member). These types of closed channel cross sectional shapes have been found to be advantageous because they provide strength and rigidity to the formed workpiece, and further can easily provide vertically and horizontally oriented side surfaces that can facilitate the attachment of other components thereto.
Hydroforming is a well known metal working process that is commonly used to deform closed channel structural members into desired shapes. Hydroforming employs pressurized fluid to deform the closed channel workpiece into conformance with a die cavity having a desired shape. A typical hydroforming apparatus includes a stationary portion (typically referred to as a bed) having a first die section secured thereto, a movable portion (typically referred to as a slide or ram) having a second die section secured thereto, and an actuating mechanism for selectively moving the slide toward and away from the bed. The die sections have cooperating recesses formed therein that together define a die cavity having a shape corresponding to a desired final shape for the workpiece. When the slide is moved toward the bed, the die sections engage one another so as to enclose the workpiece within the die cavity. Although the die cavity is usually somewhat larger than the workpiece to be hydroformed, movement of the slide toward the bed may, in some instances, cause some mechanical deformation of the workpiece. In any event, the workpiece is then filled with a fluid, typically a relatively incompressible liquid such as water. The pressure of the fluid within the workpiece is then increased to such a magnitude that the workpiece is deformed into conformance with the die cavity. As a result, the workpiece acquires the desired final shape. When the slide is moved away from the bed, the die sections are spaced apart from one another to allow the deformed workpiece to be removed and the next workpiece to be deformed to be inserted therebetween.
Because the traditional method of manufacturing the workpiece using a conventional mechanical press has been in widespread use for decades, most manufacturers of these types of workpieces have acquired a relatively large number of such mechanical presses. The monetary investment in these mechanical presses is quite substantial. Thus, although the process of hydroforming closed channel structural members has been found to possess a number of desirable characteristics, some manufacturers have moved slowly to adopt it because of their prior monetary investment in mechanical presses. Also, the acquisition of hydroforming machines requires an additional substantial monetary investment, which has further slowed the widespread adoption of hydroforming by some manufacturers. Thus, it would be desirable to provide an improved structure for a mechanical press that can adapt it to perform a hydroforming operation on a workpiece.